One of the requirements for injection molding of thermoplastic material into usable objects is to provide an effective means for heating of nozzles through which the molten thermoplastic is supplied. For certain molding equipment such as runnerless molds, the nozzles are located inside the mold, with limited space available for heater clamp mechanisms. Nozzles used for this purpose typically have a cylindrical body to which heat is supplied by a helical element placed to surround and come into contact with the surface of the nozzle. For maximum heat transfer, an outer housing in the form of a piece of split tubing is used to compress the heating element against the nozzle, with edges of the tubing being forced together mechanically so as to provide clamping action. The heating element nozzle and housing in many cases are located in a blind hole with little or no access for adjusting screws at right angles to the nozzle axis. The clamping mechanism used to force edges of the tubing together thus should be operable from an end, rather than from a side, position with respect to the tubing.
Various approaches to end-operated mechanisms for such heater clamps are disclosed in prior patents. U.S. Pat. No. 4,859,176, issued Aug. 22, 1989, to Meyer, discloses an heater clamp with an adjustment screw that rotates about an axis parallel to the heater. The device of this patent has a clamp tube disposed about a heater element and clips that extend partially around the tube with adjustment screws used to pivot the clips to act on cam-type members formed on the tube. U.S. Pat. No. 4,968,247, issued Nov. 6, 1990, to Olson, is directed to a heater clamp actuated by an axially extending cam pin that has a cam portion mounted in a loop formed from an edge portion of the housing tube. Upon rotating the pin, edges of the housing are forced together by cam action, tightening the housing around the heater. These clamping devices present disadvantages in that the Meyer approach involves a more complex manufacturing requirement with a larger number of more complex parts, and the device of the Olson patent, with its cam moving from unengaged to fully engaged with only a 180.degree. turn of a wrench, is more subject to the cam loosening due to vibration.